Understanding Apo B vs Lp(a): What's the Difference?
Apo B is a structural protein found on the surface of all "bad" cholesterol particles (like LDL), while Lp(a) is a specific type of cholesterol particle that contains both Apo B plus an additional sticky protein called apolipoprotein(a) attached to it—making Lp(a) essentially a modified, more dangerous version of LDL. 1
The Basic Structure
Apo B (Apolipoprotein B):
- Think of Apo B as a name tag that sits on the surface of cholesterol-carrying particles 1
- Every single LDL particle (the "bad cholesterol") has exactly one Apo B molecule on it 1
- Measuring Apo B tells you how many total "bad" cholesterol particles are floating in your blood 2
- It's like counting the number of delivery trucks carrying cholesterol, rather than weighing the cargo 2
Lp(a) (Lipoprotein(a)):
- Lp(a) is a complete cholesterol particle that looks like LDL but has an extra protein (apolipoprotein(a)) glued onto it with a chemical bond 3, 1
- This extra protein makes Lp(a) stickier and more likely to get trapped in artery walls 4
- The lipid core (the cholesterol inside) is virtually identical to regular LDL 1
- Because Lp(a) contains one Apo B molecule, it gets counted when you measure total Apo B 5
Why This Matters for Your Heart
The danger level is dramatically different:
- Lp(a) is approximately 6-7 times more dangerous than regular LDL particles on a per-particle basis 6, 7
- Lp(a) accumulates in artery plaques more than twice as much as regular LDL does 4
- Once Lp(a) gets into the artery wall, 83% of it becomes tightly bound and difficult to remove, compared to only 32% of regular LDL 4
Risk thresholds differ significantly:
- Elevated Lp(a) is defined as levels >30 mg/dL or >75 nmol/L 3, 8
- This affects 20-30% of the global population—over one billion people worldwide 3
- Your Lp(a) level is determined by your genes and stays relatively stable throughout your life 8
How They Respond to Treatment
This is a critical difference:
Apo B (and regular LDL) responds well to standard treatments:
- Statins effectively lower Apo B by increasing the liver's ability to clear these particles 1
- PCSK9 inhibitors also reduce Apo B levels 1
Lp(a) is stubbornly resistant to most treatments:
- Statins do NOT lower Lp(a) levels, even though they lower other Apo B particles 3, 1
- This is because Lp(a) uses different clearance pathways involving multiple receptors (SR-BI, LRP1, plasminogen receptors) rather than just the LDL receptor 3, 1
- Niacin reduces Lp(a) by 30-35% and is currently the most recommended medication specifically for Lp(a) reduction 8
- Lipoprotein apheresis (a filtering procedure) can reduce Lp(a) by up to 80% 8
The Measurement Confusion
A common pitfall: When you get standard cholesterol testing, the "LDL cholesterol" number includes cholesterol from both regular LDL and Lp(a) particles 3, 1
- Lp(a) is composed of 30-45% cholesterol by mass, and this gets counted as "LDL-C" 3
- If you have high Lp(a), your reported LDL cholesterol may overestimate your true LDL and underestimate your actual risk 3
- This is why measuring Apo B alone may considerably underestimate risk in people with elevated Lp(a) 6
Who Should Get Tested
Lp(a) measurement is recommended for: 3, 8
- People with premature heart disease (before age 55 in men, 65 in women)
- Family history of premature heart disease or elevated Lp(a)
- Familial hypercholesterolemia
- Recurrent cardiovascular events despite optimal cholesterol treatment
- ≥5% 10-year risk of fatal cardiovascular disease
Important caveat: You generally only need to check Lp(a) once in your lifetime since it's genetically determined and doesn't change 8
The Bottom Line for Risk Assessment
In practical terms:
- Apo B tells you the total number of all atherogenic particles (including Lp(a))
- But if your Lp(a) is high, each of those Lp(a) particles carries about 6-7 times more risk than the other particles counted in your Apo B 6, 7
- A novel metric called "risk-weighted Apo B" has been proposed: Risk-weighted ApoB = ApoB + (Lp(a) × 6) to account for this difference 6